Fuse



R. B. LYONS Oct. 4, 1966 FUSE Filed May 11, 1965 I NVENTOR ROBERT 5. LYONS W of fab AGENT United States Patent 3,276,373 FUSE Robert B. Lyons, Granada Hills, Calif, assignor to Atlantic Research Corporation, Fairfax County, Va., a corporation of Virginia Filed May 11, 1965, Ser. No. 454,952 Claims. (Cl. 102-27) This invention relates to novel pyrotechnic fuses. More particularly, this invention relates to pyrotechnic fuses capable of providing relatively long time delays between ignition of the fuse and initiation of the device which is to be actuated by the fuse.

Time-delay fuses find use in a variety of applications where it is desirable that the person igniting the fuse have sufiicient time to remove himself from the immediate vicinity before the fuse initiates some device such as an explosive charge. To date, small, inexpensive fuses capable of providing relatively long time delays have not been commercially available. To obtain such time delays, either expensive, relatively complex mechanical devices or long sections of conventional pyrotechnic fuses have been required. The use of long, bulky lengths of con- Ventional fuse is particularly undesirable under circumstances requiring that the fuse be as inconspicuous as possible.

Accordingly, it is an object of this invention to provide novel pyrotechnic fuses suitable for providing time delays for a variety of purposes. Another object of this invention is to provide compact fuses capable of providing relatively long time delays. A more particular object is to provide a fuse, comprising a plurality of fuse segments, which is constructed in such a manner that the desired number of such segments may be readily separated to provide for an accurately predetermined time delay. Other objects and advantages will be apparent from the drawings and the following detailed description.

Referring to the drawings, FIGURE 1 is a schematic illustration of a fuse segment representing an embodiment of this invention,

FIGURE 2 is a schematic illustration, partly in section, of a fuse representing another embodiment of this invention,

FIGURES 3A, 3B, and 3C are illustrations of a variety of separating means used in certain embodiments of this invention, and

FIGUR ES 4 and 5 illustrate fuses of this invention provided with means to facilitate ignition thereof.

Basically, this invention comprises a spiral fuse segment in which a pyrotechnic material is provided with a spiral burning path. In one embodiment of this invention a plurality of such segments are combined in such a manner that in operation the segments are successively ignited.

As illustrated in FIGURE 1, the basic fuse segment 1 of this invention comprises a flame barrier layer 2 and a pyrotechnic layer 3, coaxially, spirally wound so that successive turns of the flame barrier layer are disposed between successive turns of the pyrotechnic layer. Thus, the pyrotechnic material burns in a spiral path, the length of which is equivalent to the length of the uncoiled spiral. It is seen that this arrangement permits incorporation of a relatively long length of pyrotechnic fuse in a small volume.

The pyrotechnic layer can be any well-known pyrotechnic fuse composition such .as, for example, black match, quick-match, and mixtures of metal or metal alloy fuels with inorganic oxidizer salts or metal peroxides. The pyrotechnic layer may be in the form of loose or compressed powders, however, an integral composition having a binder is preferred for reasons of physical stability. Pyrotechnic layers, comprising cloth or paper impregnated with, for example, a slurry of metal-oxidizer composition, are particularly satisfactory for use in this invention. Such impregnated material can be attached to the flame barrier layer with an adhesive, if desired.

The purpose of the flame barrier layer is to prevent flame transfer between adjacent turns of the pyrotechnic layer in the spiral segment. Thus, the material and thickness thereof used for the flame barrier layer will be related to the burning characteristics of the pyrotechnic layer. Materials such as glass, glass fiber, metals, asbestos and the like, may be used with various pyrotechnic compositions. The flame barrier layer can be coated with various burning inhibitors or coolant compounds such as sodium carbonate, if desired, to further insure that flame transfer between adjacent pyrotechnic turns does not occur.

The spiral faces of the fuse segments can be similarly coated to further confine the burning path of the pyrotechnic layer. If this is done, it may be desirable to remove the coating from, or not apply it to, the portion of the pyrotechnic layer where burning is to be initiated.

The burning time of the spiral fuse will be dependent on the spiral length of the pyrotechnic layer and the particular pyrotechnic composition used. A wide range of burning times may be obtained by varying these factors.

Another embodiment of this invention comprises a plurality of the above-described fuse segments in combination with separating means which permit successive ignition of the fuse segments. In the embodiment shown in FIGURE 2, the segments 1 are axially aligned and separated alternately by first separating means 4 having a central opening 5 to permit flame transfer between the inner portions of segments separated thereby and by second separating means 6 having peripheral openings 7 to permit flame transfer between outer portions of the segments.

FIGURES 3A, 3B, and 3C illustrate various embodiments of second separating means 6. It is seen, therefrom, that the term opening is meant to encompass any configuration which will cause flame transfer at the desired location. For example, the peripheral perforations may be notches 7, as shown in FIGURES 3A and 3B, which can be of any desired shape, perforations 9, as shown in FIGURE 3C, located near the periphery of the separating means, and the like.

The separating means must be of such thickness and material as to prevent flame transfer between fuse segments separated thereby except at the point where the opening is located. Materials similar to those suitable as flame barriers in the spiral segments can generally be used for separating means. If desired, a pyrotechnic composition or conventional fuse can be located in the opening of the separating means to facilitate flame transfer between segments. However, this is not essential since heat transfer from a burning segment through the opening is generally sufficient to ignite the next segment.

Preferably, the spiral faces of the fuse segments are intimately juxtaposed against the separating means. Such an arrangement further confines the burning of the pyrotechnic layer to the desired spiral path and restricts ignition of successive segments to the portion of the pyro technic layer exposed by the opening in the separating means. Thus, precise ignition of successive segments is obtained and burning times can be accurately predicted.

As shown in FIGURE 2, the fuse may be provided with encasement means 8 for the segments 1 and separating means 4 and 6. Preferably, the encasement means is severable with conventional cutting means, such as a knife. This permits cutting off a length of encasement containing the proper number of segments to provide any desired time delay. Suitable encasement means can be formed of plastic, paper, cloth, metal foil, and the like. If the outer turns of the encased spiral segments are pyrotechnic layers, the encasement means should be of relatively nonflammable material so as not to propagate ignition of the fuse along the outer edge. Generally, however, the outer turns of the segments will be of flame barrier material and the choice of encasement means will be relatively unlimited. Irradiated polyolefin tubing provides a particularly satisfactory encasement means since it can be thermally shrunk around the fuse segments and separating means. If thin tubing is used, the number of fuse segments in a length of tubing and the points at which they abut sepana-ting means can be determined visually or by feel, as, for example, by running ones finger along a length of the tubing. Alternatively, or additionally, the location of segments and separating means in the encasement can be indicated by appropriate external markings. The desired number of segments can be conveniently separated by cutting the encasement means at a point where a fuse segment abuts a separating means.

In operation, a fuse segment, when ignited at its outer portion, burns inwardly along a spiral path until the path terminates at the central opening 5 in a first separating means 4. The flame is then transferred to the central portion of the next fuse segment which burns spirally outwardly to the outer portion of the segment where flame transfer occurs across a peripheral opening 7 in a second separating means 6 to the outer portion of the next segment.

Fuses of this invention can be ignited by any conventional means such as a flame, spark, or hypergolic chemical.

The time delay provided by a segment can be varied by choice of the point at which the segment is to be ignited. Obviously, the maximum delay is obtained, by ignition at one end of the spiral path of the pyrotechnic layer. Ignition of the pyrotechnic layer at a point between the ends of the spiral path results in an intermediate time delay. In order to facilitate ignition of a fuse segment at the desired point, the segment can be provided as shown in FIG- URE 4, with a cover means 11, having an opening 12 at the desired ignition point. Thus heat transfer to the segment from a match or other conventional ignition source, will be confined to the area exposed by the opening. Covers having openings at different points can be readily interchanged to provide varying time delays as desired for specific purposes. Alternatively, a portion of the segment can be bent into a convenient position for ignition or the segment can be provided with a conventional fuse extension 13, as shown in FIGURE 5,

Although this invention has been described with reference to illustrative embodiments thereof, it will be apparent to those skilled in the art that the principle of this invention can be embodied in other forms within the scope of the appended claims.

I claim:

1. A fuse comprising a plurality of segments, each of said segments comprising a coaxially wound pyrotechnic layer and flame barrier layer, successive turns of said flame barrier layer being disposed between successive turns of said pyrotechnic layer to provide a spiral burning path for said pyrotechnic layer, the axis of each of said segments being aligned along the axis of said fuse, successive segments being separated by separating means, said separating means having an opening at a terminal portion of the burning path of one of the successive segments separated thereby to effect flame transfer to the next successive segment.

2. A fuse according to claim 1 wherein said separating means has a centrally located opening to effect flame transfer between inner portions of successive segments.

3. A fuse according to claim 1 wherein said separating means has a peripherally located opening to effect flame transfer between outer portions of successive segments.

4. The fuse of claim 3 wherein said serially arranged segments are contained within a peripheral encasement.

5. A fuse comprising a plurality of serially arranged segments each of said segments comprising a coaxially, spirally wound pyrotechnic layer and a flame barrier layer, successive turns of said flame barrier layer being disposed between successive turns of said pyrotechnic layer to prO- vide a spiral burning path for said pyrotechnic layer, the axis of each of said segments being aligned along the axis of said fuse, successive segment being separated alternately by first separating means and second separating means, respectively, said first separating means having a centrally located opening to effect flame transfer between inner portions of segments separated there-by, said second separating means having a peripherally located opening to effect flame transfer between outer portions of segments separated thereby.

References Cited by the Examiner UNITED STATES PATENTS 36,172 8/1862 Sawyer 10272 432,259 7/1890 Bennett 10272 830,948 9/1906 Wieser 102-852 2,743,580 5/1956 Loeb. 10249 BENJAMIN A. BORCHELT, Primary Examiner.

V. R. PENDERGRASS, Assistant Examiner. 

1. A FUSE COMPRISING A PLURALITY OF SEGMENTS, EACH OF SAID SEGMENTS COMPRISING A COAXIALLY WOUND PYROTECHNIC LAYER AND FLAME BARRIER LAYER, SUCCESSIVE TURNS OF SAID FLAME BARRIER LAYER BEING DISPOSED BETWEEN SUCCESSIVE TURNS OF SAID PYROTECHNIC LAYER TO PROVIDE A SPIRAL BURNING PATH FOR SAID PYROTECHNIC LAYER, THE AXIS OF EACH OF SAID SEGMENTS BEING ALIGNED ALONG THE AXIS OF SAID FUSE, SUCCESSIVE SEGMENTS BEING SEPARATED BY SEPARATING MEANS, SAID SEPARATING MEANS HAVING AN OPENING AT A TERMINAL 